The present invention relates to antennas for use in a wireless communications system and, more particularly, to a high performance/capacity, low profile telecommunications antenna.
Typical cellular systems divide geographical areas into a plurality of adjoining cells, each cell including a wireless cell site or “base station.” The cell sites operate within a limited radio frequency band and, accordingly, the carrier frequencies employed must be used efficiently to ensure sufficient user capacity in the system.
There are many ways to increase the call carrying capacity, the quality and reliability of a telecommunications antenna. One way includes the creation of additional cell sites across a smaller geographic area. Partitioning the geographic area into smaller regions, however, involves purchasing additional equipment and real estate for each cell site.
To improve the efficacy and reliability of wireless systems, service providers often rely on “antenna diversity”. Diversity improves the ability of an antenna to see an intended signal around natural geographic structures and features of the landscape, including man-made structures such as high-rise buildings. A diversity antenna array helps to increase coverage as well as to overcome fading. Antenna polarization is another important consideration when choosing and installing an antenna. For example, polarization diversity combines pairs of antennas with orthogonal polarizations to improve base station uplink gain. Given the random orientation of a transmitting antenna, when one diversity-receiving antenna fades due to the receipt of a weak signal, the probability is high that the other diversity-receiving antenna will receive a strong signal. Most communications systems use a variety of polarization diversity including vertical, slant or circular polarization.
“Beam shaping” is another method to optimize call carrying capacity by providing the most available carrier frequencies within demanding geographic sectors. Oftentimes user demographics change such that the base transceiver stations have insufficient capacity to deal with current demand within a localized area. For example, a new housing development within a cell may increase demand within that specific area. Beam shaping can address this problem by distributing the traffic among the transceivers to increase coverage in the demanding geographic sector.
All of the methods above can translate into savings for the telecommunications service provider. Notwithstanding the elegant solutions that some of these methods provide, the cost of cellular service continues to rise simply due to the limited space available on elevated structures, i.e., cell towers and high rise buildings. As the user demand has risen, the cost associated with antenna mounting has also increased, largely as a function of the “base loading” on the cell tower, i.e., the moment loads generated at the base of the tower. Accordingly, cell tower owners/operators typically lease space as a function of the “sail area” of the telecommunications antenna. It will, therefore, be appreciated that it is fiscally advantageous for service providers to operate telecommunications antennas which have a small, faired, aerodynamic profile to lease space at the lowest possible cost.
As a consequence of the aerodynamic drag/sail area requirements of the antenna, it will be appreciated that the various internal components thereof, i.e., the high and low-band radiators, will necessarily be densely packed within the confined area(s) of the antenna housing. The close proximity of the internally-mounted, high and low-band radiators can effect signal disruption and interference. Such interference is exacerbated as a consequence of the bandwidth being transmitted by each of the high and low-band radiators.
For example, a first radiator can produce a resonant response in a second, adjacent radiator, if the transmitted bandwidth associated with the first radiator is a multiple of the bandwidth transmitted by the second radiator. As the bandwidth differential approaches one-quarter (¼) to one-half (½) of the transmitted wavelength (λ), a first radiator which is transmits in this range may be additionally excited by the energy transmitted by the second radiator. This combination causes portions of the transmitted signal to be amplified while yet other portions to be cancelled. Consequently, the Signal to Noise Interference Ratio, (i.e., SINR) grows along with the level of white noise or “interference.”
Accordingly, there is a constant need in the art to improve the capacity, i.e., the number of mobile devices serviced, reliability and performance of the cell phones operated by a particular telecommunications system provider.
The foregoing background describes some, but not necessarily all, of the problems, disadvantages and shortcomings related to telecommunications antennas.